This invention relates to a two-cycle engine of the crank chamber preloading type in which a crankcase, a cylinder head and a cylinder interposed between the crankcase and the cylinder head for containing a piston are clamped together and secured in place by a plurality of clamping members, such as bolts, studs, etc., penetrating the cylinder, and more particularly it is concerned with a scavenging system of the two-cycle engine of the type described.
A two-cycle engine of the crank chamber preloading type is known in which a crank chamber defined by the crankcase and a combustion chamber defined by the cylinder, the upper surface of the piston and the cylinder head are made to communicate with each other through at least one scavenging passage. This type of engine is sometimes referred to as a triple-port, two-cycle engine because the cylinder is formed in its wall with three types of openings including a suction port, an exhaust port and at least one scavenging port.
Proposals have hitherto been made to form at least one ancillary scavenging port in this type of two-cycle engine in addition to the scavenging port formed in the wall of the cylinder, for the purpose of increasing the scavenging efficiency of the engine. However, some disadvantages are associated with two-cycle engines of the prior art. In some engines, the provision of an ancillary scavenging port has had no effect in greatly increasing scavenging efficiency. In some engines where scavenging efficiency has been greatly increased by the provision of an ancillary scavenging port, the size and weight of the engines have increased. In some engines, the provision of an ancillary scavenging passage communicating the ancillary scavenging port with the crank chamber has resulted in the need to alter the configuration of the crankcase.